Spine osteosynthesis instrumentation for an anterior approach

ABSTRACT

The instrumentation comprises at least two blocks (1) adapted to transversely interconnect two rigid rods (2, 3) axially slidable in these blocks which are provided with bone anchorage screws (7, 8) suitable oriented and slides (4, 5) which are slidable in longitudinal recesses (6, 7) receiving the respective rods (2, 3) which may be in this way clamped by the slides after the latter have been completely closed. Each block (1) has in the transverse direction from the anterior part to the posterior part a curved general shape corresponding to the antero-lateral anatomy of the vertebral bodies, the interior surface being consequently concave while the exterior surface is convex. The instrumentation obtained by the assembly of two blocks (1), anchorage screws and stiffening rods (2, 3) forms a very stable rectangular structure restoring the axial continuity of the vertebral column, avoiding correction losses and facilitating the consolidation of the bone graft.

The present invention relates to a spinal osteosynthesis instrumentationfor an anterior approach.

In the field of spinal instrumentation, instrumentation for a posteriorapproach has been widely explored and still remains an interestingsolution in many pathological cases.

However, this technique has the drawback of not permitting direct accessto the vertebral bodies, which often limits the use thereof andencourages an exploration of another approach, such as the anteriorapproach.

Although it is much more delicate and complex than the instrumentationfor a posterior approach, the instrumentation for an anterior approachopens up a wider field of investigation. It is becoming necessary toinvestigate this field despite the fact that this approach requiresconsiderable technical means and environment in the hospital and aspecific training of very highly specialized orthopaedic surgerypractitioners.

Depending on the vertebral level to be reached, several techniques ofaccess by an anterior approach are at present practiced. They are:

Transpleural thoracotomy in the thoracic region,

Thoraco-phrenolumbotomy in the thoracolumbar region,

Lumbotomy in the lumbar region.

For each of these techniques, the approach on the left side of thevertebral column is preferred despite the proximity of the aorta, owingto the presence on the right side of the vena cava which is more fragileand less easy to move than the aorta.

However, the extension of the large vessels along the vertebral bodieshas repercussions on the mounting of an instrumentation.

The technique by the anterior approach of the dorsolumbar spine isemployed:

either for correcting a scoliosis and maintaining its correction,

or for treating a kyphosis with a large radius of curvature or anangular kyphosis.

Some surgeons are afraid of this technique; however, it is acknowledgedto favour the treatment of certain pathologies. It is even indispensablein certain cases.

Whatever be the surgical schools of thought formed around spinalinstrumentation, all surgeons acknowledge the following advantages ofthis technique:

Obtainment of an improved derotation of the vertical column and animproved correction of dorso-lumbar scolioses;

Obtainment of an improved instrumental stabilization, an improvedcorrection of cyphoses, and an improved nerve decompression;

Direct viewing of the vertebral part to be treated in the anteriorregion and in the median region of the column;

Use of a relatively short length of instrumentation and fusion;

Higher fusion rate, approaching a value on the order of 95%;

Reduced medullary risks owing to a direct approach to the marrow and thenecessity of distraction by a posterior action.

These advantages are of course not exhaustive and there could also bementioned: an improved decompression, the non-destruction and thereforethe preservation of the posterior stabilizing elements such as themuscles and ligaments, etc.

Resulting from the interest of the development of instrumentation for ananterior approach, many technical propositions have been made which maybe resumed as follows:

Devices employing plates or the like fixed at the ends of the latter tothe vertebrae located on each side of the vertebral region to betreated;

Devices employing rods, usually two rods, stiffened therebetween bytransverse bars to which they are fixed thus forming a rectangularframe.

Each of the proposed structures has its specific advantages but also itsdrawbacks, with the result that the considered instrumentation is not orrelatively rarely employed.

Two known examples may be mentioned:

French patent 2651992 (8912187, inventor J. M. LAURAIN) proposes the useof a rigid plate. Such a device corresponds to the specific requirementsof fractures and tumors and of the degenerative field, but is hardlysuitable for vertebral deviations.

French patent 2653413 (9001970, inventor J. DUBOUSSET) proposes the useof two metal rods fixed along the vertebral column and interconnectedtransversely by two rigid bars, which imparts to the instrumentation arectangular frame arrangement.

This solution is well suited to the problems of spinal deviations, butdoes not satisfy all the technological and surgical requirements.

In particular, the large number of parts making up the instrumentationimplies a relatively long operating time and consequently thisinstrumentation, although effective, is costly, which hinders itsextension and marketing. In brief, the instrumentation for an anteriorapproach is very delicate and represents for the surgeons a high riskthat technological innovation must attempt to reduce as far as possible.

Therefore, an object of the invention is to provide an instrumentationwhich permits overcoming these shortcomings and therefore treating,indifferently in a completely satisfactory manner, fractures and tumoursas well as spinal deviations.

The invention provides an instrumentation which comprises two rigid rodsparallel to each other or contained in parallel planes, at least twoblocks adapted to transversely interconnect said rods in such mannerthat they are axially slidable and revolvable about themselves in saidblocks, said blocks being provided with means for clamping the rodsagainst rotation and translation, and bone anchorage elements for saidblocks.

Two blocks and the two associated rods thus make up a rectangular frameaffording all of the required stability for restoring the axialcontinuity of the vertebral column, avoiding correction losses, andfacilitating the consolidation of the bone graft.

According to an embodiment of the invention, each block has in atransverse direction, from an anterior part toward a posterior part ofthe vertebral bodies, a generally curved shape corresponding to theantero-lateral anatomy of the vertebral bodies, the interior surfaceintended to be applied on a vertebral body being therefore concave whilethe exterior surface is convex.

According to other features:

The concave surface of the anterior part facing toward the vertebralbody has a radius of curvature less than that of the exterior convexsurface of the block;

Formed in each block are two parallel longitudinal recesses forreceiving a respective rod, and a slide for clamping the rod, said slidebeing longitudinally slidable in the corresponding recess and becomingclamped on the rod at the end of its travel;

Each slide is provided with inclined lateral flanges adapted to beengaged in complementary lateral grooves in the recess, and said flangescooperate with inclined clamping ramps provided in said grooves, or,inversely, the flanges are inclined and cooperate with clamping rampsprovided in said recesses;

In a possible embodiment of the invention, the block is bent so as tohave a substantially S-shaped cross-section the two halves of whichconstitute the anterior and posterior parts, the anterior part having athickness less than that of the posterior part and being capable ofbeing inserted in a recess provided for this purpose in the vertebralbody.

Further features and advantages of the invention will be apparent fromthe following description with reference to the accompanying drawingswhich show several embodiments of the invention by way of non-limitativeexamples.

In the drawings:

FIG. 1 is a partly exploded perspective view of a first embodiment ofthe spinal osteosynthesis instrumentation for an anterior approachaccording to the invention.

FIG. 2 is a perspective view to a larger scale relative to FIG. 1 of aslide for closing the recess of the block shown in FIG. 1.

FIG. 3 is a perspective view of one of the blocks of the instrumentationshown in FIG. 1 to a smaller scale than in FIG. 2.

FIG. 4 is a partial top plan view of the instrumentation shown in FIGS.1 to 3.

FIG. 5 is a cross-sectional view taken on line 5--5 of FIG. 4.

FIG. 6 is a cross-sectional view taken on line 6--6 of FIG. 4.

FIG. 7 is an elevational view of the instrumentation shown in FIGS. 4 to6.

FIG. 8 is an elevational view of a second embodiment of the block of theinstrumentation according to the invention.

FIG. 9 is a top plan view of the block shown in FIG. 8.

FIG. 10 is a half-elevational and half-sectional view taken on line10--10 of FIG. 9.

FIG. 11 is a partial top plan view of an instrumentation according tothe embodiment shown in FIGS. 8 to 10.

FIG. 12 is an elevational view of the block and the screws shown in FIG.11, the rods being shown in cross-section.

FIG. 13 is a top plan view of a vertebra, of a block according to theembodiment shown in FIGS. 8 to 12 applied to said vertebra, and adistraction-compression tool whose end is engaged in a lateral openingin the block provided for this purpose.

FIG. 14 is an elevational view of an instrumentation according to thatshown in FIGS. 1 to 7, placed in position on a spinal segment havingthree vertebrae.

The spinal osteosynthesis instrumentation for an anterior approach shownin FIGS. 1 to 7 comprises at least two blocks 1 adapted to transverselyinterconnect two rigid rods 2, 3 which are parallel to each other andaxially slidable in said blocks. The instrumentation is shown in thevertical position viewed on the left side of the spine. The blocks 1 areprovided with means for clamping the rods 2, 3 against rotation andtranslation and comprising essentially, for each block 1, 2, two slides4, 5 movable in translation in a direction parallel to the rods 2, 3 incorresponding recesses 6, 7 provided in the blocks 1, 2.

Each block 1, 2 is also provided with a pair of bone anchorage screws 8,10 which may be placed in position by inserting them in correspondingbores 9, 11 provided in the bottom of the recesses 6 and 7. The bores 9,11, and therefore the screws 8, 10, have suitable inclinations so thatthe two screws converge at a suitable angle, preferably on the order of25°.

Advantageously, the screws 8, 10 have a conical head the taper of whichcorresponds to that of the bores 9, 11 so that, when they are placed inthe bottom of the recesses 6, 7 or in the bottom of semi-cylindricalchannels receiving the rods 2 and 3, they do not project and are blockedin axial abutment by the presence of the rod.

Cavities 55 provided in the surface of each recess (FIG. 3) facilitatethe supporting of a boring tool (not shown) providing a prior bore forthe bore 9, 11.

Each block 1, 2 has, in the transverse direction from the anterior parttoward the posterior part of the vertebral bodies on which they must beanchored by means of the screws 8, 10, a generally curved shape shown inparticular in FIGS. 5 to 7 and corresponding to the antero-lateralanatomy of the vertebral bodies. Thus, this outer surface has asubstantially convex shape from the anterior surface S1 to the posteriorsurface S2, while the interior surface S3, adapted to be applied againstthe vertebral body, is concave.

Each block 1, 2 has a substantially rectangular general shape of whichthe anterior region has a thickness less than that of the posteriorregion and the edges 12, 12a are rounded. Correspondingly, the radius ofcurvature of the anterior surface S1 is distinctly less than that of theposterior surface S2.

The upper surface (S2, S1) of each block is smooth owing to the factthat the surface of the slides 4, 5 are flush with the surroundingsurface of the block, thereby avoiding any projection. The two recesses6 and 7 extend in a direction parallel to each other and are eachadapted to receive a portion of the respective rod 2, 3: the posteriorrod 2 has a diameter distinctly larger than that of the rod 3 for areason which will be explained hereinafter. The whole of the device mustbe disposed in most cases on the left side of the spine with the rod 2in the posterior position.

Arranged in the bottom of each recess 6, 7 is a semi-cylindrical channel13, 14 whose diameter corresponds to that of the respective rod 2, 3.Further, two lateral grooves 15a, 16a and 15b, 16b are formed in thesides of each recess 6, 7 in parallel relationship. These lateralgrooves are adapted to receive corresponding lateral flanges 17, 18, 19,20 of the respective slides 4 and 5. The flanges 17, 18, on one hand,and 19, 20, on the other, are arranged in a substantially differentmanner, as can be seen in FIGS. 5 to 7, owing to the dissymmetry betweenthe posterior and anterior parts of each block 1. Consequently, the sameis true of their corresponding grooves (15a, 16a, 15b, 16b).

The flanges 17, 18 and 19, 20 are inclined at a suitable angle A (FIG.2) on the bottom of the recesses 6, 7 in the same way as theirrespective lateral grooves 15a . . . 16b which have for this purposeramps of the same inclination A as the flanges 17 . . . 20. Thus theprogressive insertion of each slide 4, 5 in the corresponding recess 6,7 in the direction of the arrows (FIGS. 1 and 4) results in aprogressive gripping of the flanges 17, 18 and 19, 20 in their grooves15a, 16a . . . and finally the clamping of the slides in the recesses 6,7. The inclinations of the flanges (17 . . . 20) are inverted on theslides 4 and 5 so that the latter are inserted in the recesses 6, 7 inopposite directions indicated by the arrows (FIGS. 1 and 4) to obtain atechnical result which will be explained hereinafter. The angle ofinclination A of the flanges 17, 18 and 19, 20 and of the ramps may bebetween about 2° and 6°.

The entry ends of the flanges (19 . . . 20) are advantageously machinedin such manner as to have chamfers or rounded edges, such as 17a (FIG.2). Correspondingly, the entry edges of the recesses 6, 7 also havechamfers not, shown in FIGS. 1 to 7 but shown in FIGS. 8 to 12 (50, 51).In cooperation with the chamfers 17a, these chamfers facilitate theinsertion of the slides 4, 5 in their recesses 6, 7.

It should be noted that the semi-cylindrical channels 13, 14 are ofcourse completed by corresponding channels 21, 22 provided in the slides4, 5 (FIGS. 5 to 7).

Each block 1 can include complementary clamping means for each slide 4,5. In the illustrated embodiment, these clamping means comprise, foreach slide 4, 5, a respective screw 23, 24 which can be inserted in anopening 25, 26 provided in the central part of the block 1 between therecesses 6, 7. The opening 25 for the screw 23 communicates through alateral passage 27 (FIG. 5) with the adjacent groove 16b of the lateralflange 19 of the slide 5. Likewise, the opening 27 of the passagebetween the opening 26 for the screw 24 and the groove 16a of the flange18 of the slide 4 is shown in FIG. 5. Each screw 23, 24 has, from oneend to the other, a screw threaded bone anchorage stem 28, a conicalportion 29 which tapers toward the screw threaded stem 28, a fracturecone 31 which tapers toward the conical portion 29, and lastly ascrewing head 32.

The end of the screw threaded portion 28 is rounded and is substantiallyflush with the interior surface S3 of the block 1. This screw threadedportion 28 is so dimensioned, as is the conical portion 29, that thelatter bears against the adjacent flange 18, 19 of the respective slide4, 5 by extending through the opening of the passage 27 (FIGS. 5 and 6).

An aperture 34 is provided in the anterior part of each block in thesurface S1 between the recess 7 and the rounded edge 12. This aperture34 is adapted to receive the rounded head 35 of adistraction-compression tool 36 (FIG. 13) which is known per se and doesnot require description.

The implantation of the block 1 or "clip-block" requires the use ofspecific ancillary devices:

Ancillary device for mounting the slides 4 and 5: on each side of theseslides, i.e. on the edges of their free ends, there is provided a notchwhich permits an effective and firm engagement of the ancillary device;

Ancillary device for mounting the block 1: an opening 37 provided in thecentral part of the block 1 (FIG. 1) facilitates the engagement;

Distraction ancillary device: the bore 34 in the anterior part of theblocks 1 permits the engagement of the distraction ancillary device 36on either one of the clip-blocks 1.

The posterior rod 2 may have a diameter of 4 to 7 mm while the anteriorrod 3 has a smaller diameter of 3 to 6 mm. This difference between thediameters is explained by the fact that it is on the posterior rod 2that the main forces are exerted, in particular those due to derotation.On the other hand, the anterior rod 3 is subjected to smaller mechanicalforces and may consequently have a smaller diameter. Further, thisanterior rod 3 is the closest to the large blood vessels so that itsreduced diameter increases the surgical safety of the instrumentation.However, this difference in diameter is not obligatory and the two rods2 and 3 may possibly have the same diameter.

FIG. 14 shows an embodiment of the instrumentation according to theinvention constituting a short arrangement extending along a vertebralsegment of three vertebrae L3, L2, L1. The sequence of the mounting ofthe component parts of this instrumentation is the following:

A block 1 is placed on and then secured to the anterolateral side of thebody of the vertebra L3 by means of vertebral screws 8, 10. Anotherblock 1 is also placed in position and then secured in the same way tothe body of the vertebra L1, the vertebra L2 being the vertebra to betreated.

A posterior rod 2, for example having a diameter of 6 mm, is placed inthe posterior recesses 6 in the upper block and lower block. By means ofa suitable ancillary device, the posterior slides 4 corresponding to therecesses 6 are installed on their respective inclined ramps 6a, 7a andare placed in contact with the upper side of the rod 2. This rod is thustrapped in the recesses 6 of the blocks but remains movable intranslation and rotation under the action of outside forces. This is whythe position of the slides on their clamping ramps, or intermediateposition, must be such as to permit acting in complete safety on the rodwithout allowing the latter to escape from its recess. The slides areconsequently not pushed to the end of their inclined ramps.

Such an intermediate position of the slides enables the surgeon toeffect if necessary a derotation action on the vertebral column byrevolving the posterior rod 2 about itself. Corresponding to thisderotation is a new position of the rod 2 relative to the connectingrecesses 6, this position being automatically obtained in accordancewith the nature of the change brought about in the vertebral column bythe derotation effect.

Then an anterior rod 3, for example having a diameter of 4 mm, of thesame length as the posterior rod 2 in the embodiment shown in FIG. 14(no slides are shown), is inserted in the anterior recesses 7 of theupper block and lower block. As for the rod 2 and the slides 4 of therecesses 6, the anterior slides 5 are placed on their respectiveinclined ramps in such manner as to maintain the rod 3 in a trappedposition but sufficiently free to move in particular in translation.Their gripping action round the rod is therefore not complete as theyare not pushed to the end of their inclined ramps.

Thus, depending on the nature of the pathology to be treated, anintervention involving distraction or compression of the vertebraerelative to one another may be performed by the surgeon by means of theancillary device 36 or a like ancillary device the studs 35 of which areinserted in the bores 34 located in the anterior parts of the twoblocks.

As soon as the desired distraction or compression is obtained, all theslides 4, 5 of the blocks are pushed right to the ends of theirrespective ramps and thus exert on the rods 2, 3 a progressivelyincreasing gripping pressure which firmly clamps the rods in theirrespective recesses 6, 7 against rotation and translation.

As soon as the slides 4, 5 are fully clamped, the installation of theinstrumentation is finished. Owing to the constitution of the blocksaccording to the invention, the rectangulation or framing effect of theappliance, similar to that achieved by a plate, is obtained without theaddition of complementary parts such as transverse connection rods.

Lastly, in order to afford an additional safety in the clamping of therods and slides in their recesses, the screws 23, 24 are inserted in theapertures 25, 26, tightened and then broken off in the region of theirfracture cone provided for this purpose.

As concerns the constitution of the instrumentation according to theinvention, it is important to notice the reliability of the device, inparticular in the anchorage of the blocks 1 to the vertebrae. Theanchorage screws 8, 10 are indeed intentionally placed at the bottom ofthe recesses and advantageously possess a conical head (FIGS. 5 and 6)corresponding to the taper of the bores 9, 11 so that the head does notassume a projecting position in the semi-cylindrical channels 13, 14receiving the rods 2, 3.

When the instrumentation is definitively installed, i.e. aftercompletely closing the slides 4, 5, the anchorage screws 8, 10 are alsoclamped and can in no way, under the multiple effects of the movementsof the body of the patient, become detached from the vertebral column inwhich they are inserted. Their axial displacement is rendered impossibleso that, in the event of a possible fracture in any region of itslength, the two screw portions are held fast and nonetheless maintainthe block.

Note also that the slides of each rod are inserted in the same axialdirection, but for each of the rods the direction of insertion of theslides is inverted, as shown by the arrows in FIGS. 1, 4 and 11 engravedon the upper surface of the slides 4, 5. In this way, as the inclinedramps of the recesses 6, 7 are arranged to permit such an invertedinsertion of the slides of each block 1, after the slides are clamped inposition, all the forces exerted by the multiple movements of thepatient on one of the rods which tend to untighten the assembly aretaken by the other rod in the opposite direction for exerting grippingforces. They are in this way neutralized, this arrangement thereforeconsiderably increasing the reliability of the whole of theinstrumentation.

The instrumentation according to the invention has still furthertechnical advantages:

First of all, the rectangular structure obtained by the assembly of twoclip-blocks 1 with their slides 4, 5 and the two rods 2, 3, constitutesa device for the fixation and the rectangulation of the assemblyproviding an improved stabilization. In instrumentations of the priorart having rods, it was necessary for the two rods to be definitivelyfixed for placing in position a transverse connection device(rectangulation). Owing to the present invention, the rectangulation ofthe device is automatically obtained by the mounting of the anteriorconsolidation rod 3.

Strength for resisting physiological loads over a period of time,avoiding an excessively long fusion, permitting a rapid mobilization ofthe patient with no external immobilization, and avoiding an additionalfixation by the posterior approach requiring a second surgicalintervention.

Possibility of an instrumental correction in the three dimensions so asto restore the spinal profile (by a relative compression or distractionof the vertebrae), possibility of a complete correction of deviations,possibility of a complete correction of the vertebral rotation and ofthe gibbosity of the column for the reequilibrium of the latter.

Small volume not only as concerns thickness so as to avoid contact withthe large vessels, but also as concerns the amount of metal employed.For example, this thickness should not exceed 11 mm in the posteriorthird of the vertebral body and 9 mm in the middle third. This avoidsany interference with the consolidation of the bone graft.

Simplicity of positioning by the surgeon, owing to the small number ofcomponent parts making up the instrumentation. This reduces the numberof ancillary devices required and consequently the overall cost of theinstrumentation.

Facility and rapidity of implantation by the surgeon who, for thereasons mentioned before, must as far as possible reduce any risk ofneurological injury.

Flexibility of utilization permitting the instrumentation to be not onlyuniversal in its spinal application but also to be adapted to all levelsof the vertebral column, in particular from T4 to L5, with implants ofdifferent sizes and different shapes.

Considerable safety of utilization owing to the fact, in addition to theforegoing features, that each anchorage screw 8, 10, once inserted inits bore 9, rests therein in a completely trapped manner. Indeed, thecylindrical rod 2, 3 is clamped on the head of the screw 8, 10 by thecorresponding slide 5, 4 after the complete closure of the latter.Consequently, the screw is completely blocked in the axial directionand, if a transverse fracture of its screw threaded portion occurs, itsconsequences on the patient would be slight if not practically nil.

The force exerted for completely closing the slides 4, 5 is sufficientlyhigh to prevent the accidental opening of the latter owing to the actionof each longitudinal flange (17 . . . 20) and its chamfered end 17awhich permits a privileged insertion in one direction rather than in theother (see FIGS. 1 and 4). This is the reason for the provision ofarrows on the surface of the slides 4 and 5 which indicate the directionof insertion of each slide. This arrangement is made necessary by theslope of the sliding and gripping longitudinal flanges.

The upper surface of each clip-block 1 is completely smooth, inparticular in its most rounded lateral part S1 corresponding to theanterior positioning on the vertebrae. The upper surface of the slides4, 5 which is also smooth is flush with the surfaces S1, S2 of thelateral parts and of the central part of the block 1, so that noparticular element projects. This is a notable advantage of theclip-block provided by the invention.

The screws 23, 24 clamping the slides 4 and 5 afford additional safetyto the instrumentation by the tightening of their conical portions 29 onthe flanges 18 and 19 of the slides 4, 5. It concerns an additionalsafety means with respect to the clamping of the slides 4, 5 on the rodsC-D 2 and 3, since the clamping is in any case assured by the clampingof the slides on the rods. The screws 23, 24 therefore only have anadditional subsidiary effect. In order to avoid projecting from thesurface of the block 1, each screw 23, 24 is broken off in its upperpart after tightening on the block, with the aid of the fracture conicalportion 31. This fracture therefore occurs at the junction between thefracture conical portions 31 and the tightening conical portions 29, inthe weakest region. Thus each screw 23, 24 is practically hidden in theblock 1 since the fracture plane is approximately at a distance of 2 to3 mm from the surface S2 of the block 1.

In the second embodiment of the invention shown in FIGS. 8 to 13, eachblock 40 has a generally bent shape so as to have an approximatelyS-shaped cross-section. The two halves 41 and 42 of the block 40respectively constitute its posterior and anterior parts, the posteriorpart 41 having a thickness e1 greater than the thickness e2 of theanterior part 42. The two parts 41, 42 are interconnected by a centralpart 43 which extends in a general direction P substantiallyperpendicular to the plane P1 of the bottom of the recess 44 of theposterior part 41. On the other hand, the general direction P in whichthe central part 43 extends makes an angle B of less than 90° with theplane P2 of one of the sides of the bottom of the recess 45 of theanterior part 42. As in the blocks 1, semi-cylindrical channels 46, 47are provided in the bottom of the respective recesses 44, 45 andcomplementary channels 46a, 47a in the slides 4, 5, the diameters ofsaid channels corresponding to those of the rods 2 and 3. Bores 48, 49are provided in the bottom of the channels 46, 47 for receivinganchorage screws 10 and 8 respectively. Note that in FIGS. 8 and 9 theentry chamfers 50, 51 of the recesses 44 and 45 facilitate the insertionof the corresponding slides 4, 5. Further, the arrangement of the block40 is similar to that of the block 1, the same reference numerals beingused for the corresponding parts in both cases.

When the component parts of this instrumentation have been assembled(FIGS. 11 and 12), the anchorage screws 10 and 8 respectively extendthrough the posterior part 41 and anterior part 42 and make an angletherebetween on the order of 35° to 40°. The anterior part 42 is thenplaced in a vertebral recess 52 (FIG. 13) produced by the surgeon andopening onto the anterior part of the vertebra, for example L3 or L1.Thus the anterior part 42 of the clip-block 40 is inserted in thevertebral region. The angle between the posterior part 41 and anteriorpart 42 (corresponding to the angle between the two planes P1 and P2)affords additional safety to the surgeon bearing in mind the proximityof the large vessels in the anterior approach.

The edge 12 of the anterior part S1, which is slightly rounded in thetransverse direction as already mentioned, may have a radius ofcurvature of about 15 mm. This specific shape corresponds to the meanestimation of the value of the concavity of the vertebra in the regionof the implantation of the block 1, 40 on the latter. This dispositioncontributes to the obtainment of the desired stability of the whole ofthe instrumentation owing to the fact that there is in this way animproved distribution of the forces exerted by the concerned faces incontact.

As explained before, the directions of insertion of the slides 4 and 5are opposite so that over a period of time, when the patient resumes hisactivity, no loosening of the slides can occur; Indeed, the forces whichtend to loosen the slide or slides 4 clamping the posterior rod 2 (whichis used for the derotation), can be opposed or balanced by the forcestending to loosen the slide or slides 5 clamping the anterior rod 2.Experience has shown that it is desirable to clamp the slides 4 on theposterior rod 2 in the upward direction while the clamping of the otherrod 3 then occurs in the downward direction.

Such an assembly has an excellent mechanical behaviour. In strengthtests with a static and dynamic testing machine, employing the maximumforces normally produced by the human body, it was not possible todetect a loss of connection.

It must be understood that the scope of the invention is not intended tobe limited to the two described embodiments since many alternativeembodiments may be envisaged. For vertebral segments longer than thatillustrated in FIG. 14, the instrumentation may have the required numberof clip-blocks 1, for example three or four.

Likewise, it could be necessary that, as opposed to the embodiment shownin FIG. 14, the two rods 2 and 3 be exceptionally different, for examplethat the posterior rod 2 extend beyond the anterior rod 3. In this case,the rods may be fixed as previously described, and the extending portionof the rod may be fixed by at least one clip-block according to theinvention but defining a single recess 6 or 7. This block is then fixedso as to maintain the additional length of this rod, the recess forreceiving the other rod being unnecessary.

The additional means for clamping the slides 4, 5 constituted by thepairs of screws 23, 24 may comprise only a single screw per block 1,which may be inserted in a central aperture in the block. This apertureand the screw then have a diameter which is sufficient to ensure thatthe aperture communicates through lateral passages with the adjacentgrooves (16a, 16b) of the lateral flanges 18, 19 of the slides 4, 5. Thescrew is provided with a conical portion 29 positioned to engage in saidlateral passages and come to bear against the-flanges of the slides soas to reinforce their clamping in their recesses.

In this case, additionally, the aperture 34 may be advantageouslyeliminated, it being possible to carry out the distraction-compressionoperation by inserting the head of the ancillary device 36 in thecentral aperture of the screw.

What is claimed is:
 1. Spinal osteosynthesis instrumentation for ananterior approach, said instrumentation comprising:two elongated rods;at least two blocks for transversely interconnecting said rods, saidblocks defining openings for receiving said rods therein in such mannerthat said rods are axially slidable and revolvable about themselves insaid blocks; means slidably disposed within said blocks and bearingagainst said rods for clamping said rods against rotation andtranslation relative to said blocks; and wherein each block has ananterior part and a posterior part and a generally curved shape in atransverse direction from said anterior part to said posterior partcorresponding to the antero-lateral anatomy of vertebral bodies, saidblock defining a concave interior surface configured to contact avertebral body and a convex exterior surface.
 2. Instrumentationaccording to claim 1 wherein said anterior part has a thickness lessthan the thickness of said posterior part and has a rounded edge. 3.Instrumentation according to claim 1, wherein each block defines tworecesses each receiving a respective rod; andsaid means for clampingincludes a slide for each of said recesses, each slide beinglongitudinally slidably mounted in the respective longitudinal recessand becoming clamped on the respective rod at the end of the travel ofsaid slide along the respective recess.
 4. Instrumentation according toclaim 3, wherein each slide is provided with inclined lateral flanges,complementary lateral grooves are provided in the respective recess,said inclined lateral flanges being engageable in said complementarylateral grooves, inclined clamping ramps are provided in said grooves,said flanges being cooperative with said clamping ramps, said rampshaving an angle of inclination of substantially 2° to 6° relative to theaxis of the respective rod.
 5. Instrumentation according to claim 4,wherein each flange of each slide has an end which is the first to enterthe respective recess and is chamfered and said respective recesses hasan entrance which is chamfered whereby the insertion of said slides insaid recesses is guided.
 6. Instrumentation according to claim 5,wherein each slide bears an indicia indicating a direction of insertionof said slide into a respective longitudinal recess so that said endfirst enters the recess.
 7. Instrumentation according to claim 5,wherein said block bears indicia indicating a direction of insertion ofeach slide into a respective longitudinal recess so that said end ofeach slide first enters the respective recess.
 8. Instrumentationaccording to claim 4, wherein the inclinations of said lateral flangesof said slides and the inclinations of the associated clamping ramps areinverted between the two slides of each block.
 9. Instrumentationaccording to claim 4, wherein the inclinations of said ramps and flangesof said slides are oriented in the same direction for the slides of tilesame rod and in the opposite direction for the ramps and flanges of tileslides of the other rod.
 10. Instrumentation according to claim 3,comprising semi-cylindrical channels forming seats for said rodsprovided in the bottom of said recesses of said blocks and in saidslides.
 11. Instrumentation according to claim 3, wherein each slide hasa surface which is flush with an outer convex surface of the respectiveblock so that said outer convex surface and said surface of each slideare together smooth and devoid of any projection.
 12. Instrumentationaccording to claim 11, wherein each block comprises complementaryclamping means for the respective slide.
 13. Instrumentation accordingto claim 12, wherein said complementary clamping means comprise, foreach slide, a screw insertable in an opening provided in the centralpart of the respective block between said recesses, said openingcommunicating through a lateral passage with the adjacent groove of alateral flange of said slide, and said screw being provided with aconical portion positioned to engage in said lateral passage and come tobear against said flange of said slide to reinforce the clamping thereofin said groove.
 14. Instrumentation according to claim 13, wherein saidclamping screw comprises, from one end to the other thereof, a screwthreaded anchoring stem, a conical portion for clamping said slide whichtapers toward said screw threaded stem, a fracture conical portion whichtapers toward said clamping conical portion, and a screwing head. 15.Instrumentation according to claim 12, wherein said complementaryclamping means comprise a central aperture in each block, a screwinsertable in said central aperture, said aperture and said screw havinga sufficient diameter to enable said aperture to communicate throughlateral passages with the adjacent grooves in said lateral flanges ofthe respective slide, and said screw is provided with a conical portionpositioned to be engaged in said lateral passages and come to bearagainst said flanges of the slide and reinforce the clamping thereof inthe respective groove.
 16. Instrumentation according to claim 3, furthercomprising a cavity in a wall of each recess configured to receive aboring tool therethrough for boring in the vertebral body for insertingan anchorage screw In the vertebral body.
 17. Instrumentation accordingto claim 1, wherein one rod is an anterior rod and has a diameter lessthan the diameter of the other rod which is a posterior rod. 18.Instrumentation, according to claim 1, comprising an opening in ananterior part of each block for receiving a distraction-compressiontool.
 19. Spinal osteosynthesis instrumentation for an anteriorapproach, said instrumentation comprising:two elongated rods; at leasttwo blocks for transversely interconnecting said rods, said blocksdefining openings for receiving said rods therein in such manner thatsaid rods are axially slidable and revolvable about themselves in saidblocks; means slidably disposed within said blocks and bearing againstsaid rods for clamping said rods against rotation and translationrelative to said blocks; a pair of anchorage screws for each of saidblocks; and wherein each block defines two recesses each receivingrespective one of said rods and a pair of bores each intersecting acorresponding one of said recesses, said means for clamping includes aslide for each of said recesses, each slide being longitudinallyslidably mounted in the respective longitudinal recess and becomingclamped on the respective rod at the end of the travel of said slidealong the respective recess, and said pair of anchorage screws eachbeing inserted through a corresponding one of said pair of bores foreach of said blocks.
 20. Instrumentation according to claim 19, whereinsaid pair of anchorage screws are each supported in a respective one ofsaid pair of bores to subtend an angle between said pair of screws foreach of said blocks, said angle being substantially 25°. 21.Instrumentation according to claim 19, comprising semi-cylindricalchannels forming seats for said rods in said recesses of said blocks andin said slides, each bore opening onto the respective semi-cylindricalchannel receiving the respective rod so that each bone anchorage elementis trapped in its bore when said respective rod is clamped in positionby a complete engagement of the respective slide in the respectiverecess.
 22. Instrumentation according to claim 19, wherein one of saidrods has a first diameter and the other of said rods has a seconddiameter less than said first diameter.
 23. Spinal osteosynthesisinstrumentation for an anterior approach, said instrumentationcomprising:two elongated rods; at least two blocks for transverselyinterconnecting said rods, said blocks defining openings for receivingsaid rods therein in such manner that said rods are axially slidable andrevolvable about themselves in said blocks; means slidably disposedwithin said blocks and bearing against said rods for clamping said rodsagainst rotation and translation relative to said blocks; and whereinsaid block is curved in such manner as to have in cross-section asubstantially S-shape having one half which constitutes an anterior partand a second half constituting a posterior part, said anterior parthaving a thickness which is less than the thickness of said posteriorpart and being capable of being inserted in a cavity provided for thispurpose in the vertebral body.
 24. Instrumentation according to claim23, wherein one of said rods has a first diameter and the other of saidrods has a second diameter less than said first diameter. 25.Instrumentation of claim 23, wherein each of said recesses for each ofsaid blocks defines a bore therethrough configured to received ananchorage screw.
 26. Spinal osteosynthesis instrumentation for engagingat least two elongated rods to the anterior aspect of the spine,comprising:a block having a longitudinal length and defining twolongitudinal recesses along said longitudinal length, each of saidrecesses configured to receive a rod therein and defining a longitudinalaxis; means for clamping the rods within each of said recesses, saidmeans including a slide disposed in each of said recesses, said slidebeing slidably mounted in a respective longitudinal recess for travelfrom one end of said recess toward an opposite end of said recess, saidslide clamping a rod within said respective longitudinal recess alongthe travel of said slide; and wherein said block is formed from aunitary piece to define a fixed transverse distance separating said tworecesses from each other.
 27. Spinal osteosynthesis instrumentationaccording to claim 26, wherein:said block defines an opening betweensaid two recesses, said opening communicating through a lateral passagewith at least one of said recesses; and said instrumentation furtherincludes a screw engageable within said opening and having a conicalportion configured to extend through said lateral passage when saidscrew is engaged within said opening, whereby said conical portion bearsagainst said slide disposed within said at least one of said recesses.28. Instrumentation of claim 26, wherein one of said recesses is sizedto receive one of the rods having a first diameter and other of saidrecesses is differently sized to receive another of the rods having asecond diameter, said second diameter being less than said firstdiameter.
 29. Spinal osteosynthesis instrumentation for engaging atleast two elongated rods to the anterior aspect of the spine,comprising:a block having a longitudinal length and defining twolongitudinal recesses along said longitudinal length, each of saidrecesses configured to receive a rod therein and defining a longitudinalaxis; means for clamping the rods within each of said recesses, saidmeans including a slide disposed in each of said recesses, said slidebeing slidably mounted in a respective longitudinal recess for travelfrom one end of said recess toward an opposite end of said recess, saidslide clamping a rod within said respective longitudinal recess alongthe travel of said slide; and wherein said block defines at least onelateral groove along each of said elongated recesses and each of saidslides includes at least one lateral flange complementary with andslidable within a corresponding lateral groove.
 30. Spinalosteosynthesis instrumentation according to claim 29, wherein said atleast one lateral groove along each of said recesses defines a clampingramp inclined relative to said longitudinal axis of said recess, saidlateral flange of each of said slides being cooperative with saidclamping ramp to clamp said lateral flange within said recess along thetravel of said slide.
 31. Spinal osteosynthesis instrumentationaccording to claim 30, wherein said clamping ramp defined in each ofsaid recesses is inclined at substantially 2°-6° relative to saidlongitudinal axis of said recess.
 32. Instrumentation of claim 29,wherein one of said recesses is sized to receive one of the rods havinga first diameter and other of said recesses is differently sized toreceive another of the rods having a second diameter, said seconddiameter being less than said first diameter.
 33. Spinal osteosynthesisinstrumentation for an anterior approach, comprising:a first elongatedrod; a second elongated rod having a diameter less than the diameter ofsaid first elongated rod; a block for transversely connecting said firstand second rods adjacent the spine, said block defining a firstelongated recess configured to receive said first rod therein and asecond elongated recess configured to receive said second rod therein;and means for clamping said first and second rod within said first andsecond recess, respectively, against rotation and translation relativeto said block.
 34. Spinal osteosynthesis instrumentation for engagingthe anterior aspect of a patient's spine, comprising:a first spinal rodconfigured for fixation along the patient's spine; a second spinal rodconfigured for fixation along the patient's spine adjacent to said firstrod; a block transversely interconnecting said first and second spinalrods, said block defining a first elongated recess configured to receivesaid first rod and a second elongated recess configured to receive saidsecond rod; a first slide configured to slidingly engage said firstrecess to clamp said first rod between said first slide and said blockwhen said first rod is received in said first recess; and a second slideconfigured to slidingly engage said second recess to clamp said secondrod between said second slide and said block when said second rod isreceived in said second recess.
 35. Spinal osteosynthesisinstrumentation according to claim 34, wherein:said block defines afirst lateral groove along said first recess and a second lateral groovealong said second recess; said first slide includes a first flange forslidingly engaging said first groove; and said second slide includes asecond flange for slidingly engaging said second groove.
 36. Spinalosteosynthesis instrumentation according to claim 35, wherein:said firstlateral groove defines a first clamping ramp inclined relative to alongitudinal axis of said block, said first lateral flange beingcooperative with said first clamping ramp to clamp said first lateralflange within said first recess; and said second lateral groove definesa second clamping ramp inclined relative to said axis, said secondlateral flange being cooperative with said second clamping ramp to clampsaid second lateral flange within said second recess.
 37. Spinalosteosynthesis instrumentation according to claim 34, wherein said firstrod has a smaller diameter than said second rod.
 38. Spinalosteosynthesis instrumentation according to claim 34, wherein said blockdefines a first bore intersecting said first recess and furthercomprising a first anchorage screw inserted through said first bore. 39.Spinal osteosynthesis instrumentation according to claim 38, whereinsaid block defines a second bore intersecting said second recess andfurther comprising a second anchorage screw inserted through said secondbore, said first and second anchorage screws subtending an angletherebetween of about 25°.
 40. Spinal osteosynthesis instrumentationaccording to claim 34, wherein:said block defines an opening betweensaid first and second recesses, said opening communicating through alateral passage with at least one of said first and second recesses; andsaid instrumentation further includes a screw engageable within saidopening and having a conical portion configured to extend through saidlateral passage when said screw is engaged within said opening, wherebysaid conical portion bears against at least one of said first and secondslides when disposed within a corresponding one of said first and secondrecesses.